A gas flowmeter measures a flow rate of a gas by making use of a phenomenon that, for example, a propagation time or a propagation speed of an ultrasonic wave changes in accordance with a flow speed of a gas (fluid). That is, the gas flowmeter measures a flow rate of a gas by propagating an ultrasonic wave through a gas which flows in a measuring tube provided in the course of a flow passage (see PTL 1, for example).
Hereinafter, the configuration of a gas flowmeter described in PTL 1 is described with reference to FIG. 33. FIG. 33 is a view for describing a conventional gas flowmeter.
As shown in FIG. 33, the conventional gas flowmeter is configured by device body 81, ultrasonic flow rate measuring unit 88 housed in device body 81 and the like. Device body 81 is configured by upper case 82 and lower case 83 which are formed by performing press working on metal. Inlet pipe 84 and outlet pipe 85 are disposed on upper case 82. Inlet pipe 84 opens in the inside of device body 1 through cut-off valve 86. Ultrasonic flow rate measuring unit 88 is connected to outlet pipe 85 through connecting pipe 87 thus forming an L shape.
However, in the conventional gas flowmeter, outlet pipe 85 supports ultrasonic flow rate measuring unit 88 in a cantilever manner. Accordingly, ultrasonic flow rate measuring unit 88 is supported in an unstable state. Particularly, outlet pipe 85 supports ultrasonic flow rate measuring unit 88 substantially horizontally by way of connecting pipe 87. Accordingly, a moment applied to outlet pipe 85 becomes large thus making the supporting of ultrasonic flow rate measuring unit 88 more unstable. Accordingly, ultrasonic flow rate measuring unit 88 easily swings. As a result, there exists a drawback that the stable flow rate measurement cannot be performed due to such swinging of ultrasonic flow rate measuring unit 88.
To overcome the above drawback, the configuration may be considered where connecting pipe 87 and ultrasonic flow rate measuring unit 88 are fixed to device body 81 by bolts. In this case, device body 81 is formed by performing press working on metal and hence, it is necessary to make the bolts for fixing penetrate device body 81. Accordingly, it is necessary to provide a sealing material for preventing leakage of a gas through between the bolt and a periphery of a hole formed in device body 81.
However, usually, durability of the sealing material is low compared to a life of the gas flowmeter. Accordingly, there is a drawback that leakage of a gas occurs through a gap formed between the bolt and the periphery of the hole formed in device body 81 when the sealing material is peeled off.
Further, particularly in the case of a gas flowmeter for business use, it is necessary to make a gas flow through the gas flowmeter at a large flow rate. Accordingly, usually, an ultrasonic flow rate measuring unit and a flow passage member having the same flow passage configuration as the ultrasonic flow rate measuring unit are connected to a connecting pipe. That is, in the case of the gas flowmeter for business use, the plurality of members (the ultrasonic measuring unit and the flow passage member) are connected to one connecting pipe for measuring a large flow rate of gas. Accordingly, a weight load is increased so that a moment is further increased. Accordingly, the supporting of the ultrasonic flow rate measuring unit becomes more unstable. As a result, there is a drawback that stable flow rate measurement cannot be performed.